Let's see how smart you are /sci/

In a exam of 15 multiple choice questions, each student gets 3 points for each correct answer, 1 point is deducted for each incorrect answer, while he is not graded for each question that is not answered. If a student answers at least one question in the competition, the chances of getting a positive grade are:


72,41% or 83,25% or 86,74% or 91,75%